This invention relates to a hemispherical lock cylinder. More particularly, this invention relates to a hemispherical lock cylinder which is exceedingly difficult to pick or otherwise defeat.
All currently available lock cylinders in use operate on the general principle of a cylindrical plug rotating within a cylindrical shell. In the locked position, rotation is prevented by top pins which intrude into the shear line or separation between the plug and the shell. In order to operate the cylinder, the correctly "coded" key, i.e., that key having cuts which match the lengths of the bottom pins, is inserted such that the separation between the top and bottom pins coincides with the separation, i.e., shear line, between the plug and shell. At this point, the plug can be rotated in the shell.
The cylinder can be opened without a key by picking the cylinder, pulling out the cylinder, drilling the cylinder or punching the cylinder through the lock.
Cylinders are able to be picked because of inherent design or manufacturing induced weaknesses. The weaknesses allow the cylinder to be manipulated by picking. A pick set consists of spring steel tools which are of different shapes and spring steel tension wrenches. The wrench is inserted in the keyway, and pressure is exerted on the plug in a clockwise direction. Simultaneously, the pick is inserted in the keyway, and is used to raise the bottom pins so that the pins will reach the shearline. When all the pins have been successively raised to the shearline, the plug rotates in the cylinder and the lock is opened. Picking is possible because of a manufacturing weakness in the cylinder. When the pin chamber holes are drilled in the plug and shell, the drill bit wanders either to the right or left, top or bottom. As a result, the pin chamber holes at the shearline level will not lie perfectly on a common centerline. When tension is exerted on the plug, because the pin chambers are not exactly on center, the pins will reach the shearline at different points in the plug/plughole circumference. Picking, therefore, involves raising single pins up to the shearline to effect a bottom pin--top pin split which is held constant by the edge of the plug itself. When all the pins have met the shearline, the plug rotates and the lock opens. Since a thief cannot possibly know the "firing" or actuation order of the pins of the cylinder, it is necessary for him to move the pick in an up and down, in and out movement. The resultant up and down random movement of the pins coupled with the cylinder's drilling imperfections and the constant tension on the wrench opens the lock. If the action of the pick were analyzed with respect to the forces exerted on the pins, it would be evident that the plug is being subjected to the force of clockwise tension while simultaneously being subjected to the force of overlapping sine waves.
As mentioned before, another method of forced entry is to pull out the cylinder. In cylinders which are mounted with plain collars, the thief simply cuts and removes the collar, places vise grip pliers on the cylinder rim and wrenches the cylinder out of its mount. A screwdriver is then inserted in the hole where the cam, by means of which the cylinder actuates the lock, enters, and the lock is opened. Since the cylinder is anchored to the door with two 10-24 screws, the thief has only to find a method of breaking the screws to defeat the lock.
Another method of pulling the cylinder is to "slap" it out with a slapper. A slapper is a tool consisting of an axially aligned handle, weight and self-tapping screw head. When a "wrench proof" collar is employed, i.e., one that cannot be cut or which turns freely when a pliers is put on it, the thief simply screws the screw end of the slapper into the keyway, and shears the pins by slamming the weight against the handle. The plug, which is attached to the cam, comes out and the lock can then be opened with a screwdriver.
As mentioned above, yet another method of forced entry is to drill the cylinder. A hole is drilled at the shearline which destroys both sets of pins and allows a screwdriver to be placed in the keyway to turn the lock.
Finally, punching the cylinder through the lock is by far the most violent method of defeating a lock. Since most locks are fastened to doors from one side, it is possible to place a bar, i.e., cold chisel, to the cylinder face and punch it through the lock body itself. The lock body then just swings freely, allowing entry.
Characteristically, cylinders have been designed to mate with existing equipment, as evidenced by the fact that the external dimensions of the Leubbers cylinder, patented in 1896, are the same as those in use today. Additionally, all the cylinders in use today involve the eccentric rotation of a cylindrical solid within a cylindrical solid. Further, each cylinder has been designed to frustrate one or two methods of forced entry, while leaving the lock mechanism vulnerable to alternate methods of forced entry. Thus, a Medeco brand cylinder, probably the best available prior to the present invention, while being drill and pick resistant, can be pulled or punched.
For the purpose of making lock cylinders more pick resistant, complex keys and keyways for manipulation of plural sets of pins have been suggested in the prior art, such as U.S. Pat. Nos. 570,032; 1,500,883; 2,166,690; 2,197,673; 2,318,887; 2,620,649; 3,167,943; and 3,938,358. The fact of the matter is, however, that even with such more complex locks, picking devices need merely be inserted linearly into the keyways and there manipulated in the manner hereinbefore described.
Accordingly, it is an object of the present invention to provide a lock cylinder which is particularly pick resistant and which is, also, resistant against being defeated by pulling, drilling or punching.
It is a further object of the present invention to provide a novel key blank and the resultant keys cut therefrom for operating the novel lock cylinder of the present invention.
Other objects and advantages of the invention will be apparent from the following description thereof.